Abarth 500 Boost Limit

The car is at the tuners at the moment and there's an obstacle.

If I were comfortable with tuning it and had the necessary gear I absolutely would learn myself but this time round I figured leave it to someone who knows better than me.

The tuner has come up against an issue where mechanically everything is up to the job and the target of 1.4bar can be achieved at a portion of the rev range but at higher revs it's being limited to 1bar. He's certain it's a map issue and has made adjustments to everything he can but can't find out why the limit still exists.

Granted that's like saying please help me fix a problem you can't see, hear or feel so my question is, is this a common and time consuming issue to overcome? And could there possibly be a suggestion I can give without telling him how to suck eggs? It's the stock ECU and he's using a complete mappack and winols software.

From my limited and very much lacking tuning knowledge my first thought is there's one map he hasn't changed, could it be he's just missed one?

Hi,

James when you say it is being limited to 1 bar does it misfire or just won't push more than one bar out of the turbo or another issue ?

things to check would be blow off valve leaking/blowing off causing a boost leak

inlet manifold split causing it to lose boost at higher rpm

wastegate opening when it shouldn't ( manually hold it closed with regulated air or a with tools.

I think the factory turbo are pretty small on them, might be at or close enough to choke flow on the compressor that exhaust manifold pressure is overcoming the gate.

Called away for work so sorry chaps bit of a late reply.

So no misfire, no leaks anywhere be that on the pipework or any relief valves, wastegate and bov tested and holding fine, mechanically he's certain everything is as it should be and it makes the target boost at the mid range rpm which is 1.4bar but then drops off and holds steady at 1bar for higher rpm, 1bar was the factory defined limit in the ECU.

The turbo is capable of quite a bit more than we're utilising, as it's not the standard diddy IHI one, I've got the car back and it runs spot on so in one respect it's job done, 330nm torque in a 1.4L 900kg car is enough to keep me happy. It's just always nice to really understand why somethings happening but the tuner is sure it's a limit in the ECU somewhere, and I don't have the knowledge enough to help pinpoint the problem.